A typical force transducer generates an output signal which corresponds to an input force. The input force is applied at or near the free end of a leaf spring flexure or beam cantilevered from a fixed support. A force so applied causes a corresponding angular displacement of the beam about the fixed support. The output signal corresponding to the angular displacement of the beam from a null or neutral position is produced by strain gauges bonded to the beam.
An input force applied at or near the free end of a beam of constant cross-sectional area produces a stress which decreases from a maximum at the fixed support. The maximum allowable stress is limited by the material properties of the beam. The average stress, which determines the resolution of the transducer, will necessarily be less than the maximum stress.
U.S. Pat. No. 4,424,717, which is incorporated herein by reference, discloses a force transducer for producing an output signal in proportion to the magnitude of an input force wherein an equal and opposite force is produced by a beam assembly comprising a compound leaf spring flexure having opposed outer sections, anchored in and cantilevered from a fixed and a movable base respectively, which gradually decrease in crosssectional area to a thin middle section wherein the movable base is constrained to linear displacement from a null or neutral position by having the force applied along a line normal to and passing through the center of the thin middle section and transmitted to the movable base through a rigid connection.
In situations in which extreme accuracy is required it is important that the input force be very accurately applied to the center of the beam. The accurate positioning required to accomplish this can be difficult to attain in the above prior art device wherein the beam assembly is received in a separate, movable base member to which the force is applied.
Also, because of the two-piece construction of the prior art device the outside dimensions of the assembly are relatively large, resulting in a significant empty volume within the assembly. Since the empty volume is filled with oil, and certain performance characteristics of the transducer are dependent on the oil volume, it is advantageous to reduce the empty volume to a minimum.
Because of the foregoing, it has now become desirable to develop an extremely accurately aligned beam assembly for a force transducer.